How do I keep the dirt from sticking to my shovel while packing dirt?
Sometimes, this is inevitable with the kind of dirt you are using. Sometimes you have to wait for the right building conditions. Also it can happen if you use mud that has clay in it.
In Texas Gumbo it helps to have a 5 gallon bucket of water to dip shovel head before each scoop of dirt. Cooking spray sounds like a good idea. Wonder about reapplication and price? Maybe dump cheap olive oil in water bucket??
I usually put something on top of the dirt before packing it. A garbage bag, burlap sack, old t-shirt, etc. Makes it much easier, and lighter to carry to the trail. Something like landscape fabric would be perfect.